Inkjet devices discharge an ink from a coating head having multiple nozzles while controlling the amount of the ink. Inkjet devices are widely used for drawing any figures, characters, etc. on surfaces of paper or plastics.
For drawing figures and characters, high-resolution image quality has been required. For production of the devices, it is required to form a highly precise and even functional film. Therefore, with regard to inkjet devices, it is required that even amounts of inks are stably discharged from multiple nozzles in the coating head over time.
Therefore, with regard to the inkjet device disclosed in JP-A-2008-289983, it has been proposed that the pressure inside the coating head is controlled to always be constant, thereby attempting stabilization of ink-discharge. In this inkjet device, a supply tank that supplies an ink to a coating head, and a recovery tank that recovers the ink from the coating head are provided with pressure-control units for controlling the pressure inside the tanks, and the pressures inside the respective tanks are controlled so that the pressure inside the coating head is maintained constant. Thus, by continuously maintaining the pressure inside the coating head constant, the shape of the liquid surface in the discharge port of the nozzle in the coating head can be stabilized, thereby achieving stabilization of ink-discharging.
Furthermore, in the inkjet device disclosed in the JP-A-2012-96524, an ink-supplying pipe and an ink-drawing pipe are connected to a coating head. The ink is drawn into the ink-drawing pipe from the ink-supplying pipe through the coating head. It has been proposed that, according to such a system, discharge of the ink is carried out, while the ink is circulated therein, to thereby achieve stabilization of discharge of the ink.
In the above inkjet device, pressure sensors are installed inside the pipe that supplies the ink to the coating head, and the pipe that draws the ink from the coating head, and the ink is circulated while values indicated by the pressure sensors are adjusted. By circulating the ink therein, air bubbles and extraneous materials inside the coating head are caused to move from the inside of the coating head to the ink-circulating pathway. Thus, when the ink is discharged from the coating head, influences of air bubbles and extraneous materials can be eliminated, thereby realizing stable discharge of the ink.